1. Field of the Invention
The present invention relates to a frame structure suitable for a small-sized snowmobile.
2. Description of Related Art
A device for steering and suspending a ski as a steering member disposed at a front portion of a snowmobile is disclosed, for example, in (1) Japanese Patent Laid-Open No. Sho 61-163081, and (2) Japanese Patent Laid-Open No. Hei 3-189289.
The device disclosed in Japanese Patent Laid-Open No. Sho 61-163081 describes a snowmobile of a type including right and left skis, wherein steering arms are fixed to supporting pipes of right and left dampers and are connected to each other by a tie rod. The right and left skis are steered by simultaneously steering the right and left dampers in the same direction, to thus steer the snowmobile.
This technique is suitable for a relatively large sized snowmobile, similar to a small-sized four-wheeled buggy, of a type including a right and left steering skis, in which a frame including a supporting portion of a steering portion is relatively large.
In this snowmobile, a steering shaft is supported not by a frame member but by a stay or the like extending from the frame.
Accordingly, a steering shaft supporting portion must be disposed separately from the frame member, so that the entire frame structure including the steering shaft supporting portion becomes large and complicated and also the number of parts constituting the frame structure is increased. Such a frame structure is not suitable for a small-sized snowmobile.
The device disclosed in Japanese Patent Laid-Open No. Hei 3-189289 describes a small-sized snowmobile of a normal motorcycle using a frame similar to that of a motorcycle, in which one ski is provided on a portion equivalent to a front wheel of a motorcycle and is supported by a front fork.
A steering shaft of the front fork is turnably supported by a head tube having the same front structure of a frame of a normal motorcycle.
In a small-sized snowmobile, the frame structure described in Japanese Patent Laid-Open No. Hei 3-189289 is preferred for reducing the size of the snowmobile. However, for a snowmobile of a type in which a driver operates the snowmobile in a standing state, the frame structure of a motorcycle type in which a head tube is provided at a front end portion has the following problems.
For the snowmobile of the type in which a driver operates the snowmobile in a standing state, it is desired to lower the position of head members for supporting steering arms. In this regard, the structure of Japanese Patent Laid-Open No. Hei 3-189289 is disadvantageous in that the position of the front portion of the frame, particularly, the head tube is lowered so that the suspending member for the ski is close to the head tube. As a result, it becomes difficult to ensure a sufficient stroke of the suspending member and also the head tube may interfere with an engine and the like because of the lowered head tube.